Air conditioning control system



March 7, 1944. C R H 2,343,467

AIR CONDITIONING CONTROL SYSTEM Filed June 28, 1941 15 MWa/ Afiorney- Patented Mar. 7, 1944 AIR CONDITIONING CONTROL SYSTEM William L. McGrath, Philadelphia, Pa", assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application June 28, 1941, Serial No. 400,283

23 Claims.

The present invention relates to air conditioning control systems wherein it is desired to main tain predetermined conditions of temperature and humidity over a relatively wide range of load, that is, for example, where the temperature of the air to be conditioned may vary from 50 F. to 100 F. dry bulb and the relative humidity of the air to be conditioned may range from to 90%.

Commonly in the past in this type of air conditioning work wherein dehumidification must be accomplished at dew pointtemperatures below freezing, refrigerated brine sprays have been used. Control of equipment using brine sprays is difficult and equipment is subject to deterioration. Furthermore, the brine must repeatedly be regenerated as it absorbs moisture.

The primary object of my invention is to obviate the use of brine sprays entirely by using a refrigerating coil for dehumidiflcation purposes,

operating it at temperatures below freezing and defrosting it by the use of heated sprays when necessary. My invention comprehends the use of fresh water for the heated sprays and when humidiflcation of the air is required rather than dehumidification, the temperature of the heated sprays being controlled by means responsive to the requirements for humidification. When sensible cooling without dehumidification is required, the refrigerating coil is operated at temperatures above freezing. When the coil is operating at temperatures above freezing, the sprays may be operated without being heated in order to improve the heat exchange between the air being conditioned and the coil.

The refrigerating coil orunit may preferably be the evaporator of a direct expansion refrigeraoperation.

The primary object of my invention as referred to above is to provide an air conditioning control arrangement wherein dehuniidification is to be the control of means responsive to the moisturecontent of the air being conditioned, the last mentioned means controlling fresh water sprays for humidifying purposes, the arrangement providing for heating and turning on the sprays at maximum temperature when defrosting of the coil is required.

Another object of the invention is to'provide an air conditioning control arrangement utilizing a direct expansion refrigeration coil-with face and by-pass dampers associated with the coil controlled by means responsive to the moisture content of the air being conditioned, the last mentioned means controlling operation 'of the direct expansion coil and also a set of heated .fresh water sprays which are operated when humidification rather than dehumidiflcation is required. 1

Another object of my invention is to provide an arrangement wherein a direct expansion refrigeration coil is utilized in an air conditioning control system, the coil having fresh water sprays associated therewith and face and by-pass dampers, the operation of the coil-being controlled by a dry bulb thermostat for the purposes of removal of sensible heat from the air and by means responsive to the moisture content of the air for controlling the coil for purposes of removal of latent'heat from the air, the moisture responsive means controlling the face and by-pass dampers tions as respects temperature and humidity. The

space may be aroom or other compartment having'a floor represented by the numeral H. The right hand nd-of-the duct I0 is connected to the inlet of a-fan l2 driven by. an-electric motor 13,

the outlet of the fan being connectedto a discharge duct H which discharges into thespace Withinthe duct at an intermediate point is a septum or a partition Ii which divldes the duct into a main air passage and a by-pass passage, the latter passage being above the partition l5. Located within the mainair passage driven by an electric motor l3 by means of a by an electric motor.

belt IS, the compressor and motor being mounted on a common base 23. The motor I8 is of atwo speed type having electrical speed changing mechanism including electricalterminals designated C for common and F and S for fast and slow respectively. The discharge of the compressor is connected to a condenser 2| by a pipe 22 andthe" condenser II has a liquid receiver 23 associated therewith which is connected to the v. evaporator l3 by pipe 24. interposed in the pipe -24 at the inlet of the evaporator I6 is a thermostatic expansion valve 21 of a known type which.

is arranged-to control the amount of superheat of the refrigerant at the outlet of the evaporator.

Valve 21 includes a pressure chamber comprised in part of an expansible wall member, this pressurechaniber being connected to a thermal bulb 23 by means or a capillary tube 29, the thermal bulb 23 being .disposed in intimate heat exchange relationship with the outlet of the evaporator l6.

Also interposed in the pipe 24 ahead of the expansion valve 21'is' a solenoid type stop valve 3|. The valve 3| is of the on and or! type and is controlled by an electrical winding within the portion 32 of the valve. The outlet of the evaporator I3 is connected to the suction side of the compressor by ,a pipe 33. s

Ahead of the evaporator l3 as respects the flow of air through the duct I is a pipe 35 having spray nozzles whereby water may be sprayed into the air'stream and over the evaporator l5. The-pipe 35 is connected to the discharge of a circulating pump 36 which is driven The suction side of the pump 35 is connected to a pipe 31 which extends into a fresh water'tank or sump 33. The portion of the duct adjacent the pipe 35 and evaporator I is depressed as shown at 33 so as to form modulating valve 43 which includes an electric proportioning operating motor of the type disclosed in detail in the patent of D. G. Taylor No. 2,028,110. The motor of this valve is supplied with power by meansof wires 44 and 45. This valve is controlled by a proportioning controller like the one shown in the Taylor patent and this controller and its manner of controlling the steam valve 43' will be presently described.

Located in the duct l3 beyond the evaporator |3 is 'a steam coil 53 for purp ses of reheatin the air which has been, cooled and dehumidifled by the evaporator I3. Steam is admitted to the valve 50 through a pipe 5| and the condensate is withdrawn. therefrom through a pipe 52. Interposed in the pipe 5| is a valve 53 similar to the valve 43 and which 'is operated in a similar manner. Power for operation of the motor of valve 53 is supplied through wires .54 and 55 and this valve is.controlled also by a proportioning controller which will presently be described.

The flow of air past the sprays '35 and the evaporator I6 and through the by-pass duct is controlled'by' means of'iace and by-pass dampers designated by the numeral 51. These dampers are controlled by an electric proportioning dam-- p er motor 53 which is of the same type as the motor of the Taylor patent previously referred to. The damper motor 53 has a crank arm 53 which is connected to the face and bypass dampers'by a stem 63. The damper motor 53 5 operates an auxiliary switch by means of a cam 6| on the shaft 62'of the damper motor. The cam 6| has a single dwell which actuates a pivoted lever 63 carrying the switch which is a mercury switch 64. As will presently be described, the mercury switch 54 is normally open but is closed when the damper 58 operates in a manner to cause a relatively smaller proportion of the air to pass over the evaporator l6.

The damper motor 53 is controlled by an elecl5 trio proportioning controller designated generally by the numeral 61. This controller is the same general type of proportioning controller as disclosed in the previously mentioned Taylor patent. The proportioning controller 31 is arranged to control both the damper motor 58 and .the steam valve 43 and therefore the controller has two proportioning resistances designated by the numerals 53 and 33. Numeral 13 designates a pivoted slider which'is adapted to slide over the resistance 33 and numeral 1| designates a pivoted slider adapted to slide over the resistance 63. Numeral 12 designates an operating lever connected to both of the sliders 1|! and 1|, the righthand of the lever 12 being connected to a pivoted bell crank lever 13. The other arm of the bell crank lever 13 is normally urged against the op crating stem of an expansible and contractlble bellows 14 by means of a coil spring 15. The expansible and contractible bellows 14 is connected to a thermal bulb 16 of a wet bulb temperature controller by means of a capillary tube 11.. The

bulb 16 is filled with the usual volatile liquid and draped over the bulb is a piece of porous fabric 13, the lower edges of which are disposed in a pan of water 19. The piece of fabric 13 acts as a wick causingwater to travel upwardly through the fabric by capillary attraction to wet the bulb 15. There is continuously a certain amount of evaporation from the wick depending upon the relative humidity of the atmosphere in the space and this evaporation has a cooling effect upon the bulb 16 so that the temperature of the bulb is depressed below the dry bulb temperature of the space by an amount depending upon the moisture content of the air. Also, the pressure developed within bellows 14 obviously is proportional to the wet bulb temperature of the atmosphere in the space and the bell crank lever 13 is accordingly rotated about its pivot depending upon the wet bulbtemperature in the space. Upon a. rise in the wet bulb temperature, the bellows." expands rotating bell crank lever 13 in a counter-clockwise direction and moving the lever 12 and sliders 10 and 1| to the left. Upon a fall in wet bulb in an opposite manner.

damper motor 53 by a wire 3| and the slider 13 is connected to the damper motor 53 by a wire 32. The right end of resistance 33 is connected to the damper motor 53 by a wire 34. With the parts in the position shown, the wet bulb temperature is at substantially a desired value and slider 13 is in the mid point of resistance 58. The face and by-pass dampers 51. are in an intermediate position causing desired proportions of air to pass over the sprays and evaporator and through the by-pass. When the wet bulb temperature rises, indicating-that the humidity'is too great, slider 13 is moved to the left so as to reduce the voltage temperature the sliders are moved to the right drop between wires BI and 92 as respects that between wires 02 and 84 which'has the eil'ect of causing motor 58 tooperate in a direction to move the face and by-pass dampers into a position wherein a smaller proportion of air is passed over the evaporator I6 and a greater proportion is passed through the by-pass. Upon a fall in wet bulb temperature indicating that humidification rather than dehumidification of the air is required, the slider I is moved to the right reducing the voltage drop between wires 82 and 84 as respects that between wires 8| and 82 and this causes the motor 58 to operate in an opposite direction'tending to move the face and by-pass dampers into a position wherein a greater portion of air is passed over the evaporator I8 and a smaller proportion through the by-pass.

The right-hand end of resistance 69 is connected to the motor of valve 43 by a wire 81 and a wire 88. The left end of resistance'69 is connected to a contact strip 89, the extremity of which is connected to the operating motor of valve 43 by a'wire 90. The slider 'II is connected to a fixed electrical contact 95 forming part of'an electrical relay 92 by means of a wire 93. The relay '92 comprises a winding 94 having an armature associated therewith which is attached to the switch blade 9| and which moves the blade into engagement with fixed contact 95 when the winding 94 of the relay 92 is energized.

When the winding 94 is deenergized, the blade 9| engages with a fixed electrical contact 96. The fixed electrical contact 95 is connected to the operating motor of valve 43 by means of a wire 98 and wire 88. The switch blade 9| is connected to the operating motor of valve 43 by a wire 91. Relay 92 also includes a switch blade 41 operable thereby which engages a fixed contact 48 when the winding 94 is deenergized. From the foregoing, it is to be seen that contact 95 controls the connection between slider 1| and valve 43 and that when switch blade 9| engages contact 96 a direct connection is produced between control wires 91 and 88. This latter connection, as will presently be described, causes the valve 43 to be operated to a wide open position. The valve 43 is normally controlled-by the slider II and resistance 69 and with the parts in the position shown, except assuming that blade 9| is engaging contact 95. the valve is in a closed position.

Upon a fall in humidityas evidenced by a fall in wet bulb temperature below'the intermediate or desired value, the slider II moves to the right decreasing the voltage drop between wires 93 and 81 as respects that between -wires'90 and 93 and this has'the effect of operating 'valve 43 in anopening direction to admit steam to the coil 4|. The coil 4| therefore heats the water in the tank 38 and as will presently be described, this heated water I may be sprayed through thespray nozzles 35 so The compressor motor I8. is controlled in partthrough a double coil relay designated by the numeral I00. This relay comprises a-pull-in wind- There is ing I02 anda bucking winding IOI. an armature associated with the windings which is connected to a pair of switch blades I03 and I04 which moves to the left into engagement with fixed electrical contacts I05 and I08 respectively, when the ull-in winding I02 is energized and v 3 the bucking winding IOI is not. Power for operation of'the relay I00 is supplied by a stepdown transformer I01 having a primary winding I08 and-a secondary I09 having a fewer number 6 of turns. Power for the primary winding I08 is supplied through wires III) and III. :The control of the relay I00 will be described presently. The valve-53 and the relay I00 are controlled by a combined prbportioning and on and oil controller responsive to dry bulb temperature and designated by the numeral H2. The controller 2 includes a proportioning. resistance ,I I3 over which a slider H4 i adapted to sweep. Numeral I I5 designates an elongated arm which is connected to the mid point of the slider H4 and the left end of which is pivoted to a pivoted bell lever H8 is normally urged into engagement with the operating stem of an expansible and,

contractible bellows I" by a coil spring I24, the interior of the bellows being connected to a thermal bulb M8 by a capillary tube I I9. The bulb I I8 is filled with vaporizable liquid as usual which expands and contracts in accordance with dry bulbtemperature in the space, the bellows III expanding and contracting proportionately. Numeral I designates a pivoted switch blade movable between fixed electrical contacts I2I and I22, the blade I20 normally being biased into engagement with the contact I2| by a coil .spring I23. The end of the arm 5 is disposed adjacent the blade I20 and when the bellows III expands a predetermined amount, the bell crankv lever I I6 is rotated in a clockwise direction moving the arm II5 and-slider II 4 to the right until the end of arm I I5 engages the blade I20 moving it away from contact I2I' and into engagement with contact I22. Operation of blade I20 occurs at the extremity of travel of slider H4. The left end of resistance H3 is connected to the operating motor of valve 53 by wire I25 and the slider H4 is connected to the valve motor by a wire I25. The right end of resistance I I3 is connected I to a relatively short contact strip I21, the extremity of which is connected to the operating motor of valve 53 by a wire I28. With the conand the slider H4 is at the mid point of resist- When the dry ance H3 and contact strip 2|. bulb temperature falls, the bellows III contracts moving bell'crank lever IIB in a counter-clockwise direction and moving arm I I-5 and slider II4 to the left along resistance I I3. .;This reduces the voltage drop between wires.l25 and I26 as respects 'that'between wires I28 and I28. This causes the motor of valve 53 to operate in a direction to open the valve admitting more steam to the reheat coil so asto raise the temperature of the air and to cause the dry bulb temj perature in the space to return to the required value wherein the slider II4 is in the position shown. When thedry bulb temperature rises, the bellows l|5 expands thus causing slider 4 to move to the right which reduces the voltage drop between wires I28 and I28 as respects that between wires I25 and I25. which causes the valve 53jto be operated toward closed position, and it is in fully closed position when the slider II4 moves on to contact strip I21. Upon a further rise in dry bulb temperature, the blade I20 is then moved away from contact I2I and 'into engager'nent with contact I22. The arrangement is preferably such that the blade I20 engages contact I22 at a temperature substantiall one degree presently be described.

The variable speed windings of the motor I8 and the solenoid valve 3I are controlled by'a relay designated by the numeral I 3|, this relay comprising a winding I32 having an armature associated therewith which is connected to movable switch blades I32 and I34 which are moved into engagement with fixed electrical contacts I35 and I36 when the winding I3I is energized. When the winding I3I is deenergized, the switch blade I34 normally engages a fixed electrical contact I31.

The motor of pump 36 and the fan motor I3 are controlled by a relay designated by the numeral I40. The relay I46 comprises a winding I having an armature associated therewith which is attached to movableswitch blades I42 and I43 which are moved to the right, blade I43 engaging fixed electrical contact I45 when the winding I is energized. Blade I42 normally engages contact I44 for normally keeping fan I2 in operation through the following circuit for fan motor I3: from wire I12 to contact I44, blade ,I42, wire I13, motor I3 to wire I14, the wires I12 and I14 being connected to a suitable source of power not shown.

The motor of pump 36 is controlled directly by a relay designated by the numeral I41. The relay I41 comprises a winding I46 having an armature associated therewith which is attached to a movable switch blade I48 which is .moved to the left into engagement with a fixed electrical contact I50 when the winding I46 is energized.

The controls for the system additionally in-. cludes suction pressure responsive switches designated by the numerals I52 and I53. Switch I52 comprises an expansible and contractible bellows II, the interior-of which is connected to the suction pipe 33 of the compressor by tubes I54 and I55. The bellows I5I has an operating stem which normally engages a pivoted lever I56 carrying a mercury switch I51 having electrodes at its right end. The lever I56 is normally biased against the operating stem of the bellows nected to the'bellows I66 by a capillary tube I1l.

The bulb I10 contains a volatile liquid which expands and contracts in accordance with the temperature of the evaporator I6 causing the bellows I66 to expand and contract accordingly.

The controller I65 is so adjusted that the bellows by a coil spring I58. The bellows I5I expands in response to rising suction pressure and normally maintains they switch I51 open. The bellows I5I contracts upon fall in suction pressure, and at a relatively low value of suction pressure, which will occur when the evaporator has frosted .up so as to seriously impair its heat exchange I51 and brings properties, closes the switch about defrosting of the evaporator as will presently be described. The switch I53 comprises an expansible and contractible bellows I60, the interior of which is connected to the suction pipe 33 of the compressor by -the tube. I55. The bellows I60 has an operating stem into engagement with which a pivoted switch lever I6I is normally urged by a coil spring I62. The lever I6I carries a mercury switch I63 having electrodes at its left end. The switch 263 is closed when the suction pressure rises to a predetermined relatively high value so as to rotate the lever I6I into closed position of the switch. The switch I63 is opened when the suction pressure falls to a predetermined relatively low value.

The relay I41 controlling the motor of pump 36 is controlled by a temperature responsive controller I65. The controller I65 comprises an expansible and contractible bellows I66 having an operatin stem normally engaging a pivoted le- I66 will be expanded sufficiently to cause closure of mercury switch I68 by rotation of the lever I61 in a counter-clockwise direction, when the temperature of the evaporator affecting the bulb I10 is substantially 35 F. When the evaporator is operating at temperature below this, that is temperatures which may be below freezing, the pump 36 is not operated inasmuch as it would not be desirable to spray fresh water onto .the evaporator and permit it to freeze thereon.

The arrangement of my invention is set up to provide for substantially continuous operation of the system except when it is necessary to defrost the evaporator. With the parts in the position shown, the wet and dry bulb temperatures are at substantially the desired values. If now there should be a rise in'wet bulb temperature, the slider 10 will be moved to 'the left in the manner already described and the face and bypass dampers will be readjusted to a position causing a smaller proportion of air to pass over the evaporator I6 and a greater proportion'to be by-passed. The controller 61 may be set so that when the slider 10 is at the mid point of resistance 68, the wet bulb temperature is 59 for example. When the slider 10 has been moved a slight amount to the left out of this position, the

motor 56 is operated sufficiently to cause cam 6| to .close the mercury switch 64. Closure of this switch completes a circuit energizing the relay I3I as follows: from the line conductor I16 through a wire I11 to the mercury switch 64,

wire I18, winding I32, wire I19 and wire I back to-lineconductor I8I, the line conductors I16 and I8I being connected to any suitable source of p0wer not shown. Upon energization of relay 'I3I, blade I 33 engages contact I35 and a circuit is completed for energizing and opening the solenoid valve 3| as follows: from line conductor I16, through wire I82, wire' I83, valve 3i, wire I84, wire I85, wire 220, switch blade I33, contact I35, wire I86 and wire I80 back to line conductor I8I.- When solenoid valve III is opened, the suction pressure rises causing closure of switch I53,

that is, closure of mercury switch I63, or such switch may already be closed as will appear hereinafter. Closure of this switch together with energization of relay I3I causes completion of the high speed circuit of motor I8, this circuit being as follows: from line conductor. I16

through wire I82, wire I68, wire I69, mercury completing a circuit for relay I41 as follows: from line conductor I95 to a wire I96, the winding I48, through wire I91, mercury switch I68,

wire I98, wire I99, back to line conductor 200.

by-pass dampers 51 are moved into a position wherein a still greater proportion of air is bypassed and a smaller proportion is passed over the evaporator I6, the refrigerating system continuing to operate at high speed. Stop means may be provided to limit the damper movements.

As the wet bulb temperature rises as described, the slider 1| moves over onto the contact strip 89 without operating the motor of-valve 44, this valve remaining in a closed position.

, During this dehumidi'fying operation just descrbed, the operation of the refrigerating system will remove a certain amount of sensible heat as well as latent heat from the air and more than likely the dry bulb temperature in the space being conditioned will tend to fall. If this occurs, the bellows II1 will contract in the manner abovedescribed moving the slider II4 to the left along resistance II3, causing the valve 53 to be operated in an opening direction so as to admit steam to the reheat coil 50. The steam coil 50 will reheat the air which has passed over the evaporator tending to bring it back to the proper dry bul'b temperature and causing the controller II2 to reassume, the

position shown in the drawing. That is, the controller II2 will control the dry bulbtemperature of the air. g

The above described dehumidifying operation will normally tend to cause the wet bulb temperature to drop back to the desired value, the slider 10 moving back to the mid position of resistance 68. As the wet bulb temperature returns to the desired value, the face and by-pass dampers will be returned to the position shown in the drawing and the mercury switch 64 will be opened so as to interrupt operation of the refrigerating system. When the mercury switch 64 is opened, the relay I3I is of course deenergized interrupting the high speed circuit of the compressor, and the solenoid valve 3| is closed.

When switch blade I34 engages contact I31, the low speed circuit of the compressor motor is completed as follows: from line conductor I16,

to wire I82, wire I88, wire I89, mercury switch- I63, wire I90, switch b1ade 41,'wire I9I, switch blade I34, contact I31, wire 212, the S and terminals of motor I8 and wire I93 back to line conductor I8I. Completion of thiscircuit causes operation of the compressor at low speed. This quicklypumps down the evaporator since the liquid line valve 3I is closed, causing opening of switch I63 and completestoppage of the compressor.

If the wet bulb temperature falls below the de sired value of 59, the slider 10 moves to the right along resistance 68 causing the face and by-pass dampers to be operated to a position wherein a greaterproportion of air is passed over the evaporator I6 and a reduced proportion is by-passed. At thesame time the slider 11 moves to the right alongresistance 69 causing valve 43 to be operated in an opening direction as above described, admitting steam to the coil H for heating the water in the tank 38. "The mercury switch 64 will under these circumstances be open and the increased amount of air passing over the evaporator I6, will raise its temperature to a value above 35 Realising the controller I65 to close the mercury switch" I68 the line conductors I95 and 200 being connected to a suitable source of power not shown. En-

ergization of the relay I41 moves switch blade I49 into engagement with contact I complet-' ing a circuit for the motor of pump 36 as follows:

from line conductor I95, through wire 20I, contact I50, switch blade 9, wire 202, the motor of pump 36, wire 203, wire I99back to line conductor 200. heated water from tank 38 to be pumped up through pipe 35 and discharged through the spray nozzles into the air stream passing over the evaporator I6. This heated water will serve to humidity-the air, the air taking up more moisture 'by reason of the fact that the water is heated. Continued fall in wet bulb temperature causes the steam valve 43 to be opened wider and wider so as to heat the water in tank 38 more and more. When the wet bulb temperature returns to its normal value, the slider 'II and the slider 10 are moved back to their normal positions and the valve 43 and dampers 51 will again assume their normal positions.

. The controller II2 may be so adjusted that the slider H4 is at the mid point of resistance H3 and contact strip I21 when the dry bulb temperature is 10 for example. The controller I I2 may be so adjusted that the arm II5 opens contact I2I at 71.and closes blade I20 to engage contact I22 at 72, for example. If at any time the dry bulb temperature should rise high enough so as to cause blade I20to engage contact I22, a circuit is completed for pull-in winding I02 of relay I00 When blade I04 engages contact I06, a circuit is completed for the solenoid valve 3I as follows:-

'from line conductor I16, through wire I82, wire I83, valve 3|, wir I84, wire 2I0, contact I06, blade I04, wire 2 back to line conductor I8 I. When solenoid valve 3| is opened, the suction pressure in pipe 33 rises causing closure of switch I63 in the same manner as alreadydescribed, closure of this switch now completing a circuit for the slow speed winding of motor I8, this circuit being as follows: from line conductor I16, through wire. I82, wire I88, wire I89, mercury switch I63, wire I90, switch blade 41, contact 48, wire I9I, switch blade I34, contact I31, wire 212 through the low speed and common terminals of motor I8 through wire I93, back to line conductor'I8I. The refrigerating system will now operate at low speed until the dry bulb temperature has fallen sumciently to cause blade I20 to move away from contact I22 andto engage contact I2I. When this occurs, a circuitwill be completed for the bucking winding IOI of relay I00 as follows: from secondary winding I09, through; wire 205, wire 209, contact I05, blade I03, wire 206, blade I20. contact I2I, wire 2I6,-winding IOI, wire 2I8, and wire'208 back'to secondary I09. Both windings WI and I02 will now be energized and so their Operation of the pump 36 will cause ,closes for defrosting pressor is operating athishspeedthecompressor magnetizations will neutralize each other causing the relay to drop out deenergizing both windingse Disengagement of blade III from contact I06 will interrupt the circuitof solenoid valve 3| and the compressor will then quickly pump.

down the coil causing opening of mercury switch I63 which will interrupt the circuit of the compressor motor causing it to stop.

the pipe to-be discharged through the spray nozzles and over the evaporator. The hot water being sprd'yed over the evaporator defrosts it relatively quickly. Th mercury switch I51 opens.

at a suction pressure sufllciently high to insure that the evaporator temperature has risen to a value high enough such that all the frost has when the compressor is operating at high speed in response to humidity requirements the evaporator li may become frosted up so that. its heat exchange properties are seriously impaired.

, When this occurs, the suction pressure will fall to a relatively low value causing closure of switch I52, that is, closure of mercury switch I51. when this occurs, the relays I2 and I II will be energized. The circuit for relay -92 is as follows; from line conductor III, through wire" III, wire I86, contact I", switch blade III,wire 22l, wire 22 I, winding I4, wire 222,'wire 223, mercury switch, I51, wire 224, wire lII,--wire I82, back toline conductor I16. At the same time winding III of relay I'll is energized through the following c'ircuit: from line conductor- III, through wire III, wire III, contact I", switch blade III, wire 22!, wire 22I, wire 22I,'winding III, wire 22I,'wire 223, mercury switch I51, wire 224, wire III, wire III, back to line conductor I18; when relay I2 is energized, switch blade .41 is moved away from contact II, this interrupting the circuit supplyin power to the compressor motor and causing it to been evaporated therefrom. When the mercury switch I51-opens, the re1ays92 and I are deenergized, the fan I2 is placed back in operation, the pump 36 is stopped and the valve 43 is placed back under the control of the controller 61.

During normal operationwhen the evaporator I6 is operating at a relatively high temperature, that is, when above 35 F., the controller I65 will cause operation of the pump 35 in the manner already described. Thus unheated water will be sprayed into the air stream and over the evaporator, and this water will serve to provide for '20 better heat exchange between the evaporator and the air passing throughthe duct III.

From the foregoing, it is to be seen that I have provided a system utilizing a refrigeration coil which is operated at times at temperatures below es-freezlng. The system provides-for substantially continuous operation with automatic defrosting of the refrigeration coil, the system providing for the maintainment of desirable wet and dry bulb temperatures of the air in the space being condi- 30 tioned, With the arrangement of my invention,

desirable wet and dry bulb temperaturecanbe maintained over a wide range of loads and by means of the heated sprays the refrigerating unit can be quickly and efllciently .defrostedwhen 36 necessary.

The single embodiment of my invention which 1 I have disclosed is representative, and my disclosure is to be interpreted in an illustrative rather than a. limiting sense, the invention to be so limited only in accordance with the claims stop. switch blade II is moved away from contact I6 and into engagement with contact II. Disengagement of blade II from contact II interrupts the connection of slider H to the operating motorjof valve I I and therefore interrupts control of this valve by the controller I1. Engage ment of'blade II with contact II connects wire 91 to wire, thus shunting one of the operating windings of theoperating motor of valve 43 causing the valve to move to a wide open position sothatsteamisadmittedtothecoilll atamaxappended hereto.

1 claim as my invention: 1. In an air conditioning system, in combination, refrigerating apparatus including a source of refrigerant and a cooling unit, means for passing air to-be conditioned in heat exchange relationship with the unit, means responsive to a psychrometric condition of said air controlling the refrigerating apparatus, means for spraying water so as to cause it to contact said unit, means responsive to a condition of said refrigerating apparatus incident to a need for defrosting'the imum ratefor heating the water in tank II.-

. When-relay III is ,awit'ch blade I42 is -mov'ed away from contact I interrupting the circuit of the fan motor H stopping thefan and terminating the circulation of air through the duct II. Also-when relay III is energized. switch blade I engages contact Ill completing a circuit for relay I" as follows: from line conductor Ill, through wire "I, winding llkwire 221,

contact in, switch blade m, wire :20, back to line conductor 2. when relay I" is energised.

' I switch blade m a. mum mm eng g ment with contact III, completing a circuit for the motor of pump It as follows: from line conductor III, through wire III, contact III, switch blade III,

wire2I2,themotorofpumpII.-wire2fland.

'wire II'IbacktolineconductorlII.

'Timsa istobescen tbatwhcn the switch is:

when the commotorisdecnerg'iseddhcsteamvaln IIisopencd -wide, the fan I2 isstoppcd andthc pump 20 is unit, and means for heating said water, said last condition responsive means being arranged to render said heating means operative and control the spray unit. 2. In an air conditioning system, in 'tion, refrigerating apparatus including a source water so as to hasten defrosting of the 1 of refrigerant and a cooling unit, means for passing air to be conditioned in heat exchange rela-. tionship with the unit, means for reducing the volume of air passing in'heat exchange relationship with the unit whereby the temperature of the unit may fall below freezing causing frost to accumulate on it, means for spraying water so as to cause it to contact said unit. and means responsive to the suction pressure of said refrigerating apparatus resulting from a needfor defrosting the unit,'said suction pressure responsiye means being arranged to control the spray water so as to hasten defrosting of the unit.

3. In an air conditioning system, in combination, refrigerating apparatus including a source started in operation to pump hot water through of refrigerant and a cooling unit. means for mcombina psychrometric condition of the air for operating ing air to be conditioned in heat exchange relationship with the unit, means for'reducing the volume of airp'assing in heat exchange relationship with the unit whereby the temperature of the unit may fall below freezing causing frost to accumulate on it, means'for spraying water so as to cause it to contact said unit, means responsive to a condition of said refrigerating apparatus incident to a need for defrosting the unit, means for heating said water, said lastvcondition responsive means being, arranged to control the temperature of the water so as to hasten defrosting of the unit, and means responsive to the temperature of the unit controlling said spraying means whereby water may be sprayed into said air without being heated when the unit is not in need of defrosting.

4. In an air conditioning system, in combination, refrigerating apparatus including a source of refrigerant and a cooling unit, means for passing air to be conditioned in heat exchange relationship with the unit, means responsive to a psychrometric condition of said air controlling the refrigerating apparatus, means for spraying water so 'as to c use it to contact said unit, means responsive o a condition of said refrigerating apparatus incident to a need for defrostin the unit, means for heating said water, said last condition responsive means being arranged to render said heating means operative and control the spray water so as to hasten defrosting of the unit, and means by which said last condition responsive means causes passage of air in heat exchange relationship with the unit tobe" interrupted while it is defrosting.

5. In an air conditioning system, in combina-- tion, refrigeratingapparatus including a source of refrigerant and ac'ooling unit, means for passing air to be conditioned in'heat exchange relationship with the unit, means for reducing the volume of air passingin heat exchange relationship with the unit whereby the temperature of ,the unt may fall below freezing causing frost to accumulate on it, means for spraying water so as to cause it tocontact said unit, means responsive to the suctionpressure of said refrigcrating apparatus resulting from a need for defrosting the unit, said last condition responsive means being arrangedto control the spray water so as to hasten defrosting of the unit, and means by which said lastcondition responsive means causes passageof air inheat exchange relationship with the unitftobeinterrupted while it is defrosting. 1 p

- 6. In an air conditioning system, in combination, refrigerating apparatus including. a source of refrigerant and a cooling unit, means for passing air to'be conditioned in heat exchange relationship with the unit, means influenced'by a psychrometric condition of the airfor operating said cooling unit at temperatures below freezing whereby frostaccumulates on it, means for spraying .water so as to. cause it to contact said unit, means for heating said water, and control means for interrupting operation 'of the refrigerating apparatus to defrost the unit, said control meansbeing arranged to render said heating means operative and control thespray water for hastening defrosting of the evaporator.

7. In an air conditioning system, in combina- -tion,refr.igerating apparatus including a source of refrigerant and'a cooling unit, means for passing air to be conditioned in heat exchange relationship with (the unit, means influenced by a said cooling unit at temperatures below freezing whereby frost accumulates on it, means for spraying water so as to cause it to contact said unit, means for heating said water, control means for interruptingoperation of the refrigcrating apparatus to, defrost the unit, said control means being arrangedto render said heating means operative and control the spray water for I hastening defrosting of theevaporator, and means by which said control means causes passage of air in heat exchange relationship with the unit to be interrupted when the unit is to be defrosted.

8. In an air conditioning system, incombination, refrigerating apparatus including -a source of refrigerant and a cooling unit means for passing air to be conditioned in heat exchange relationship with the unit, means responsive to the temperature and moisture content of the air for operating said cooling uhit at temperatures above and below freezing wherebyfrost accumulates on it at times, means for spraying water so as to cause it to contact said unit, means for heating saidwater, control means for interrupt-- ing operation of the refrigerating apparatus to defrost the unit, said-control means being arranged to control the temperature of said water for hastening defrosting of theyevaporator, and

means responsive to an above freezing temperature of the unit for controlling said spraying means in such manner that water may be sprayed into said air without being heated when the unit is not in need of defrosting.-

9. In an air conditioning system, in combina-- tion, air cooling means comprising refrigerating apparatus having an evaporator, means for passing air over the evaporator, means responsive to air temperature for controlling the refrigerating the air for controlling the temperature, of said water, and control means for interrupting operation of the refrigerating apparatus for de-' frosting the evaporator, said control means beingarranged to control the' spraying means and the temperature of the water forhastening defrosting of the evaporator.

10. In an air conditioning system, in combin-ation, air cooling means comprising refrigerating apparatus having an evaporator, means forpassing air over the evaporator, meansresponsive'to air temperature for controlling'the refrigerating apparatus, means for spraying 'waterso as to cause it to contact, the air being conditioned and also the evaporatonmeans'for heating said water, means responsive to'the moisture content of the air for controlling the temperature of said water, control means for interrupting operation of the refrigerating apparatusfo'r defrosting the vaporator, said control" means being arranged to control the spraying means and the temperature'of the water for hastening defrosting of the evaporator and means by which" said control means interrupts passage of air overthe evaporator when itisto be defrosted. 11. In an air conditioning system, in combina tion, means forming a duct, means for passing air through said duct, apparatus for removing sensible and latent heat from air-in said'duct,

means for normally regulating the proportion of air passed over said apparatus, meansre'sponsive regulating means to decrease the proportion of air passing over said apparatus on increase in said moisture" content, said moisture responsive means also controlling said apparatus to regulate the removal of latent heat from the air, thermostatic means responsive to air temperature controlling said apparatus to regulate the removal of sensible heat from the air, and means for heat ing the air controlled by said thermostatic,v

means; said apparatus being arranged to operate at relatively high capacity in response to said moisture responsive means and at relatively low capacity in response to said temperature responsive means.

12. In an air conditioning system, in combination, means forming a duct, means for passing air through said duct, apparatus for removing sensible and latent heat from air in said duct, means for normally regulating the proportion of air passed over said apparatus, means responsive to the moisture content of the air controlling said regulating means, said moisture responsive means also controlling said apparatus to regulatethe removal of latent heat from the air, thermostatic 'means responsive to air tempera ,ture controlling said apparatus to regulate the removal of sensible heat fromthe air, means for spraying water into the air in said duct, means for heating said water, and means by which said moisture responsive means controls said water heating means to control the temperature of the water to increase the amount of moisture to humidity of the cooled air for controlling said water heating means for increasing the temperature of said spray water upon an increased demand for moisture in the air, and

' means for controlling said water heating means and said spraying means to spray water over said device at a relatively high temperature for defrosting the device.

14. In an air conditioning system, in combination, air cooling apparatus comprising a device over which air'ia adapted to be passed for removing sensible and latent heat from the air,

means foroperating said device at temperatures causing it to become frosted, means for spraying fresh water into said air and over said device, means for heating said water, means responsive to humidity of the cooled air for controlling said water heating means for increasing the temperature of said spray water when humidiflcation of the air is required and. decreasing the temperature of said device when dehumidiflcation is required, and means for controlling said water heating means and spraying means for causing 'water to besprayed over said device at relatively high temperature for defrosting the device.

15. In an air conditioning system, in combination, aircooling apparatus comprising a device over which air is adapted to be passed for removing sensible and'latent heat from the air, means for operating said device at temperatures-causing it to become frosted, means for spraying fresh water into said air and over said device, means for heating said water, means responsive to humidity of the cooled air for controlling said water heating means for increasing'the temperature of said spray water when humidification of the air is required and decreasing the temperature of said devite when dehumidification is required, means for controlling the dry bulb temperature of the [cooled air including means controlling said deand'said spraying means for causing water to be isprayed over said device at relatively high temperature for defrosting the device.

16. In an air conditioning system, in combi- V nation, refrigerating apparatus including a source of refrigerant and a cooling unit, means for passing air to be conditioned in heat exchange relationship with the unit, means for reducing the volume of air passing in heat exchange relationship with the unit whereby the temperature of the unit may fall below freezing causing frost to accumulate on it, means for spraying water so as to cause it to contact said air'a'nd also said unit, means for heating said water, humidity responsive means controlling said air volume reducing means, temperature responsive means controlling said refrigerating apparatus, and control means for interrupting operation of the refrigerating apparatus for defrosting the unit, said control means being arranged to cause heating of the spray water for hastening defrosting of the unit.

17. In apparatus of the character described, in combination, refrigerating apparatus including an evaporator, means for passing air to be cooled over the evaporator, means for operating the evaporator at temperatures below freezing so that the evaporator becomes frosted, means for spraying water over the evaporator to increase the rate of heat transfer between the air and the evaporator, and means for heating said sprayed water in response to a decrease in suction pressure indicating that the evaporator should be defrosted. I

18. In apparatus of the character described, in combination, refrigerating apparatus including an evaporator, means for normally circulating air over the evaporator while the evaporator is operating to produce cooling, means for defrosting the evaporator including mean forspraying water over the evaporator, and control means responsive'to suction pressure normally resulting from a frosted state of the evaporator for'shutting down the refrigerating apparatus, the air circulating means, and causing the defrosting means to operate.

19. In apparatus of the character described, in combination, refrigerating apparatus including an evaporator, means for normally circulating air over the evaporator while the evaporator is operating to produce cooling, means for defrosting the evaporator including means for spraying water over the evaporator, means for heating said water and control means responsive to suction pressure normally resulting from a frosted state oi" the evaporator for shutting down the refrigerating apparatus, the air-circulating means, and causing the defrosting means to operate.

20. In an air conditioning system, in combinacrating said water heating means to heat the water when humidiflcation is desired, and air temperature responsive means for operating said cooling means at a relatively high temperature and for preventing heating of the water by said water heating means when the air temperature is too high.

21. In an air conditioning system, in combination, a cooling means, means for passing air over the cooling means, means for spraying water inv to the air, means for heating the water, means responsive to the temperature of the cooling means in control of said water spraying means to cause the spraying of the water into, the air when the temperature of the cooling means is relatively high, moisture responsive means in control of said cooling means, and water heating means for operating said cooling means to produce a relatively low temperature when dehumidification is desired and for operating said water heatin 20 over the evaporator, means for operating the evaporator at temperatures below freezing so that the evaporator becomes Irosted,,a source of water, means for heating said water and spraying it upon said evaporator, means responsive to a demand for humidiflcation in control of said last named means, and means responsive to a condition resulting from a need for defrosting the evaporator for also controlling said water heating and spraying means to cause heated water to be sprayed upon said evaporator.

23. In apparatus of the character described, in combination, refrigerating apparatus including an evaporator, means for passing air to be cooled over the evaporator, means for operating the evaporator at temperatures below freezing so that the evaporator becomes frosted, a source of water, means for heating said water and spraying it upon said evaporator, means responsive to a demand for humidification in control of said water heating and spraying means, means responsive to a condition resulting from a need for defrosting the evaporator for also controlling said water heating and spraying means to cause 25 heated water to be sprayed upon said evaporator,

and means for interrupting passage of air over the evaporator when it is defrosting.

WILLIAM L. MCGRATH. 

